Photographic process for the direct production of positive images



2,699,393 Patented Jan. 1 1 1955 PHOTQGRAPHIC PRUESS FOR THE DIRECT. PRDDUCTIQN F POSITIVE IMAGES Edith Weyde, Leverlmsen-Burrig, Germany, assignor .to

AGFA Aktiengcsellschaft fiir Photofabrikation, Leverkusen, Germany, a corporation of Germany NoDrawing. Application April 15, 1950,

Serial No. 156,230

. Cla ms- (CL 95" 3) This invention relates to a photographic process for the direct production of positive images and to new photographic materials used therein. p

it is one obiect of the invention to provide an improved photographic process for the direct production of positive images. Further objects of the invention will be seen from the description following hereafter.

In the French Patent 879,995 there is described a photographic process for the direct production of positive images. according to which a light sensitive silver halide emulsion layer, atterbeing exposed to an object, is developed in the presence of a silver halide solvent, said silver halide emulsion layer being in close contact during said developing process with a light insensitive reception layer containing nuclei for development. During this process the exposed part of the silver halide emulsion layer is developed to a negative image of the object to which it had been exposed, while at the same time part of the unexposed silver halide is dissolved by the silver halide solvent. This disssolved silver halide diffuses to the reception layer, where it is reduced to a positive image by the developer under the catalytic action of the nuclei for development present in said layer. As nuclei for developrnent there may be used for instance colloidal silver, colloidal gold, colloidal silver sulfide or other known substances which either are nuclei for development by themselves or which produce such nuclei for development during the developing process. In order to render the positive image freely visible, the silver halide emulsion layer will normally be removed from the reception layer after development. The meaning of the words negative and positive as used in the above description is relative, that means if the emulsion layer is exposed to a negative object, there will be produced a direct negative in the reception layer, whereas if the emulsion layer is exposed to a positive object a direct positive will be obtained.

The silver halide emulsions used for the production of the light sensitive layer may be silver chloride emulsions, silver chlorobromide emulsions or silver bromide emulsions containing silver chloride. The light sensitive layer and the reception layer may be arranged on separate supports, for instance on sheets of paper or on films of cellulose acetate, nitrocellulose, polyamide etc, or they may be poured one over the other on the same support. in the latter case the reception layer may be strongly hardened and poured on the support as the undermost layer, while the light sensitive layer is not hardened at all or or only Weakly hardened and poured over the reception layer, so that after development it may be removed by treating it with hot water by which the hardened reception layer is not attacked.

The above process is particularly useful for the production of positive images on both sides of a sheet-like support. This may be achieved by using a material carrying reception layers on both sides of the support. For the direct production of positive images on transparent supports by a reflectographic process there may be used materials coated on one or both sides with a reception layer and a silver halide emulsion layer, the reception layer of which may contain a dispersion of colloidal opaque particles, such as for instance colloidal ZnO, which may be removed by the developing bath or by a separate bath after the development of the material.

The developing substance and the silver halide solvent may be used in the alkaline developing solution, however it is also possible to incorporate at least one of them in either the silver halide layer or in the reception layer.

or in both. The above French Patent 879,995 discloses that the development of the silver-halide layer and of the reception layer is carried through in the presence of compounds which influence the tone of the silver deposited in the reception layer. The compounds suitable for this purpose are disclosed in the German Patent 473,000. Theyare characterized in that they form silver salts difficultly soluble in water and hypo. If the process is carried through without these compounds, the silver images formed in the reception layers are of an awkward yellow to brown colour, whereas 1 in the presence of the above compounds the tone of the positive silver images becomes almost black. However the process as disclosed in the above patent sufiers from the serious disadvantage of producing positive silver images the tone of which is transformed into black only in thedarker shades, whereas it remains yellow in the lighter shades of the image. A further disadvantageof the process is to be seen in the fact that the compounds as disclosed by theGerman gradation of the positive Patent 473,000 decrease the images.

It'lS an object of my invention to produce positive images by means. ofthe, aboveprocess, which are equally welltoned in the high lights as well as in the dark shadows and which have an agreeable gradation. Ac-' cording to my invention I employ mercaptotetra zoles as toning substances for this purpose. These compounds may be added to the silver halide emulsion layer or/and to the reception layer or/and to the developing solution. They are used in amounts of 0.0l-1 gr. per liter of de veloping solution, 0.0l-0.5 gr. per liter of molten silver halide emulsion, or 0.0l0.5 gr. per liter of a 6 per cent aqueous solution of a binding agent, as for instance gelatine, from which the reception layer will be produced. The binding agent for the emulsion layer and/ or the reception layer may be a gelatinous or a non-gelatinous substance or a mixture of both. The following mercaptotetrazoles have been found to be most suitable for the purpose defined above: mercaptotetrazoles substituted by aliphatic residues as for instance l-allyl-5-mercaptol,2,3,4-tetrazole mercaptotetrazoles substituted by aromatic or heterocyclic residues as for instance l-phenyl-S- mercapto-l,2,3,4-tetrazole of the following formula SH l=N The following example serves as an illustration of my invention.

A reception layer is produced by coating a sheet of paper with an aqueous 5 per cent gelatine solution containing 0.05 gr. of colloid silver and 0.05 gr. of 1-phenyl- S-mercapto-1,2,3,4-tetrazoles per liter. A dry silver chlorobromide emulsion layer coated on a paper support is exposed to an object. Both layers are impregnated with a developer containing per liter 20 gr. NazSzOz, 12 gr. hydroquinone, 12 gr. NaOH, 60 gr. NazSOg, 0.5 gr. KBr and pressed together by means of a pressing roll. After about one minute both layers are separated from each other. There is received a positive image in the reception layer equally well toned in the high lights and dark shadows and of agreeable gradation.

I claim:

1. In a photographic process for the direct production of positive images according to which a light sensitive silver halide emulsion layer, after being exposed to the object to be reproduced, is contacted in the presence of a silver halide developing solution and a silver halide solvent with a reception layer containing development nuclei, whereby a negative image is developed in the light sensitive silver halide emulsion layer and silver halide 1S dissolved in the unexposed areas of the silver halide layer, transferred to the reception layer and developed in this layer under the catalytic action of the development nuclei to a positive image, the improvement which comprises carrying out the development of the contacted silver halide layer and reception layer in the presence of a 5-mercapto1,2,3,4-tetrazole.

2. A photographic process according to claim 1, wherein the 5-mercapto-1,2,3,4 tetrazole used is substituted in l-position by an organic residue.

3. A photographic process according to claim 2, wherein the S-mercapto-l,2,3,4-tetrazole used is l-allyl- S-mercapto-1,2,3,4-tetrazole.

4. A photographic process according to claim 2, wherein the S-mercapto-1,2,3,4-tetrazole used is a 1- phenyl-S-mercapto-l,2,3,4-tetrazole.

5. In a photographic process for the direct production of positive images according to which a light sensitive silver halide emulsion layer containing a silver halide developing substance, after being exposed to the object to be reproduced, is contacted in the presence of an aqueous alkaline solution containing a silver halide solvent with a reception layer containing development nuclei, whereby a negative image is developed in the light sensitive silver halide emulsion layer and silver halide is dissolved in the unexposed areas of the silver halide layer, transferred to the reception layer and developed in this layer under the catalytic action of the development nuclei to a positive image, the improvement which comprises carrying out the development of the contacted silver halide layer and reception layer in the presence of a S-mercapto-1,2,3,4-tetrazole.

6. A photographic light insensitive printing material comprising a light insensitive layer of a water permeable organic colloid containing development nuclei of the group consisting of colloidal noble metals and colloidal water insoluble compounds of noble metals for the reduction of silver halide to metallic silver, and S-mercapto- 1,2,3,4-tetrazo1e.

7. A photographic light insensitive printing material comprising a light insensitive layer of a water permeable organic colloid containing development nuclei of the group consisting of colloidal noble metals and colloidal water insoluble compounds of noble metals for the reduction of silver halide to metallic silver, and 5-mercapto-1,2,3,4-tetrazole, and a silver halide solvent.

8. A photographic light insensitive printing material comprising a light insensitive layer of a water permeableorganic colloid containing development nuclei of the group consisting of colloidal noble metals and colloidal water insoluble compounds of noble metals for the reduction of silver halide to metallic silver, and S-mercaptol,2,3,4-tetrazole, and a silver halide solvent, and a silver halide developing substance.

References Cited in the file of this patent UNITED STATES PATENTS MacMillan Co., N. Y., New York (1942), page 96. 

1. IN A PHOTOGRAPHIC PROCESS FOR THE DIRECT PRODUCTION OF POSITIVE IMAGES ACCORDING TO WHICH A LIGHT SENSITIVE SILVER HALIDE EMULSION LAYER, AFTER BEING EXPOSED TO THE OBJECT TO BE REPRODUCED, IS CONTACTED IN THE PRESENCE OF A SILVER HALIDE DEVELOPING SOLUTION AND A SILVER HALIDE SOLVENT WITH A RECEPTION LAYER CONTAINING DEVELOPMENT NUCLEI, WHEREBY A NEGATIVE IMAGE IS DEVELOPED IN THE LIGHT SENSITIVE SILVER HALIDE EMULSION LAYER AND SILVER HALIDE IS DISSOLVED IN THE UNEXPOSED AREAS OF THE SILVER HALIDE LAYER, TRANSFERRED TO THE RECEPTION LAYER AND DEVELOPED IN THIS LAYER UNDER THE CATALYTIC ACTION OF THE DEVELOPMENT NUCLEI TO A POSITIVE IMAGE, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT THE DEVELOPMENT OF THE CONTACTED SILVER HALIDE LAYER AND RECEPTION LAYER IN THE PRESENCE OF A 5-MERCAPTO-1,2,3,4-TETRAZOLE. 